[sjshn]

As a fairly recently departed GitHub employee, I know with certainty that this change is primarily related to abuse. The search infrastructure (both old and new) is complicated and expensive to run, and anonymous search was abused at a remarkably large scale. DDoS against the anonymous search service was a big problem, but another was the presence of many very large search botnets that constantly scraped the site for secrets and other confidential data inadvertently made public. Long time users might remember that anonymous search was aggressively rate-limited on a per-IP basis, but the size of the search botnets grew to a scale that made this ineffective.

My personal opinion is that most enshittifying changes on GitHub are due to the proliferation of middle managers who are evaluated almost exclusively on speed-shipping net-new features at the expense of maintenance and incremental improvement of existing features.